


Under the stars is the sparkling, heart-pounding sound of the sea beat

by Baka_nekonya



Category: BanG Dream! Girl's Band Party! (Video Game)
Genre: F/F, Mainly Kasuari
Language: English
Status: In-Progress
Published: 2020-06-02
Updated: 2020-06-07
Packaged: 2021-03-03 19:13:22
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 3
Words: 3,997
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24500602
Author URL: https://archiveofourown.org/users/Baka_nekonya/pseuds/Baka_nekonya
Summary: When she was a child, Kasumi Toyama experienced the "sea beat" and she's been looking for that feeling ever since.15-year-old Kasumi is a sailor who meets a mermaid by the name of Arisa Ichigaya after falling out of her boat during a storm. Arisa is the 52nd heir to the Ichigaya throne in the kingdom of Ryuseido.This is the tale of a sailor and a mermaid, whose paths were fated to cross.
Relationships: Hazawa Tsugumi/Hikawa Sayo, Ichigaya Arisa/Toyama Kasumi, Okusawa Misaki/Tsurumaki Kokoro, Shirokane Rinko/Udagawa Ako
Kudos: 22





	1. A coincidence

A small girl stood in the silent but powerful waves of the ocean. Part of her brown hair was bundled up into tiny ponytails at the side and she wore a pink cardigan with a purple checkered skirt. She remembered that her parents warned her not to go out into the sea late at night but something about the way the waves lapped at her feet just seemed... enchanting. 

To the left, it was the sea. To the right it was the sea. Nothing could be more comforting than the notion of peace, quiet and the sound of the ocean.

The moon was shining and the stars were blazing, a perfect night sky on a perfect day. 

The girl in the sea then noticed another detail which she had left out : a single, solemn star floating about. 

Its glow was radiant, reflecting the soft glow of the moon. The star sparked something in the little girl's heart, beckoning her to take hold of it. It seemed to multiply when she picked it up. No, it didn't multiply, she merely did not notice the other stars drifting on the surface, forming a trail.

Children are rumored to be rather curious creatures, and this one proved it. She edged her way to pick up each star in her tiny hands till she could hold to no more. Desperate to keep all of them, she stuck them into her pockets, her cardigan, anywhere that could hold her treasures. 

Luckily, the line of stars stopped at a cavern before she ran out of space. Was this here before, she asked herself. Maybe her earlier expeditions were not as throughout as this one, that was why she failed to notice the cave. 

Peeking inside, she recognised the same glow the stars gave out. That prompted her to investigate further, and so she did.

Gently setting down the mass of shiny objects on a flat rock at the side, she waded into the cavern.

When the little girl came to a bend in the cave, she saw the silhouette of a person with twin ponytails on the walls. But that was not the only thing she saw. There was the shadow of a large tail.

Could it be? The child's imagination began to wander, down to the depths of an old , lost legend. It was said that mermaids used to roam freely between the land and the sea. But a terrible disease struck, forcing the mermaids into hiding. The reason is unknown to this day.

Excited, she ran into the opening of the cave to find another girl around her age. Her blonde hair was tied in twin tails and she wore rather peculiar clothes which she didn't know the name to yet. The blonde girl seemed shocked at her arrival as she was frozen in place.

Their eyes interlocked, and the brown haired girl felt something stir inside her. Hearing the gentle, rhythmic crashing of the waves led her to one conclusion. This was the sound of the "sea beat" , the sound of their hearts reflected against that of the ocean and the starry sky.

"Hello! My name is Kasumi! Nice to meet you!" The brunette flashed a toothy grin and extended her hand. Knowing that her counterpart was a mermaid did not bother her a single bit. Mermaids are cool, she thought.

The other girl mumbled shyly, "I'm Arisa... " Having someone else in her presence must have disturbed her quite a bit. 

Kasumi must have not sensed the other girl's unease as she continued energetically without missing a beat, "Are these stars yours? I found some floating at sea just now and they're very pretty!"

That seemed to have softened the mood as Arisa smiled and replied, " Really? I made these myself! I think I made a bit too much, that's why you were able to find them."

" Hey! So did you hear that sound just now when we met? It was all sparkly and heart-pounding! The 'sea beat'! You know, when you feel all sparkly inside and..." Kasumi rambled on, attempting to explain her thoughts so that Arisa would get it.

Arisa didn't, but enjoyed listening to Kasumi's explanation. 

"Um... Can-can we be friends? Not that I'm that lonely! But..." Before Arisa could say another word, Kasumi clasped her hands with Arisa's, eyes wide and sparkling.

" We're friends now, then! ...Wah! Did you hear that? I just heard the 'sea beat' again!" Kasumi exclaimed, looking at her newfound friend. Arisa seemed to agree this time, clutching onto Kasumi's hands tightly.

At that moment, Kasumi thought of a great idea. Without saying a word, she took the silver star-shaped necklace looped around her neck, and broke it into half.

"Here! Take this! This will be like our proof of friendship... or something!" Kasumi chuckled, presenting the other half of her necklace. Arisa gladly took hold of it.

Then silence ensued, each girl not sure of what to say. Arisa opened her mouth to say something, but her expression turned from joy into shock. There were suddenly loud noises of rushing water, the typical ones you would hear at a waterfall.

"L-look out! The tide-!"

Kasumi didn't have time to react. She, along with the countless stars Arisa made was swept up in the rising current. She felt her head collide with something hard and after that, nothing.


	2. A new(?) discovery

"e ...llo?… Wake up!"

Kasumi's eyes fluttered open.

Huh… I was having that weird dream again, she thought as she slowly checked her surroundings. Looks like I'm in a cave... 

The next thing that she noticed was another face above her own. She had blonde curly hair that was adorned with pearls and a weirdly shaped hair pin that looked like half a star. Then, Kasumi's eyes went further down and felt her cheeks flush red-hot. 

The other girl noticed what Kasumi was staring at and quickly moved away, embarrassed. " Quit staring at me like that! " 

Kasumi quickly sat up right, still red in the face. " S-sorry… I… Thanks for saving me. The storm was really bad last night…" She then realised something, no, a few things. 

"How did you save me? The storm-Wait, when did you- it was… where are we? What time is it… ah! Where's Aa-chan? Who-

"Slow down! I can't answer all of that at once!" The other girl yelled in exasperation. "Sheesh… So I was swimming around and then I saw you in the water-

"But wasn't it really stormy last night? Like,how-

"Could you just listen? Hmph. Look, you see this?" The blonde girl pointed to her tail half out of the water. "I am a-

" Mermaid!!!" Kasumi shouted while pointing at her light pink tail.

" Stop interrupting me!" The other girl was getting annoyed. She took a deep breath and attempted to regain her composure. "Yes, mermaids exist. But you must absolutely not tell anyone that! I saved you and brought you to this cave. Any other questions? And mind you, one at a time!"

Kasumi felt compelled to answer but her thoughts mainly consisted of bewilderment at a mermaid casually sitting next to her. 

When Kasumi was young, she liked to venture out to the ocean. There was one occasion that she found herself passed out on the beach with vague memories of a dream she never had. After explaining it with wide eyes to her sister, Asuka, she merely dismissed it as a dream. Telling others about her "dream" only brought shame and trouble. Thus, Kasumi never talked about meeting a mermaid again.

Now she can finally prove them all wrong! "Umm, so.. are there others? Like one with blonde hair that was tied up like yours?" Kasumi turned to face the mermaid.

" There are others, heck, one entire ocean filled with them. So there's a likely chance that there is another mermaid that looks like me. Why did you ask?" She replied, curious about Kasumi's sudden question. 

Kasumi was ecstatic that she asked. " When I was young I met a mermaid and I felt the 'sea beat'! It made me tingle with excitement when I heard it! You know, it's really sparkling and heart-pounding? Oh wait!" Kasumi dangled her half-star shaped necklace in front of her face. 

" Okay! I broke my necklace into half and passed half of it to her because we were friends. But then afterwards… I don't really remember. I sorta forgot her name too..."

A hint of familiarity crossed the blonde mermaid's eyes. She then averted her gaze and spoke, "Oh, that seems nice... I hope you find her."

Kasumi was oblivious to her reaction. " Hey, so what's your name? I'm Kasumi Toyama, I heard the 'sea beat' when I was a child and I've been searching for that ever since!" 

" Arisa. Arisa Ichigaya. Plus, you keep going about this 'sea beat' thing. What is it anyways?" Arisa was curious.

" Huh? Didn't I explain it just now? When you hear the 'sea beat', it makes you feel all sparkly and makes your heart pound with excitement !" 

" Haaah? I don't get it." 

Kasumi's face scrunched up in contemplation. " It's… just sparkly and heart pounding? The sea beat… you'll know when you hear it!" She gave up on trying.

" Just asking, but don't mermaids wear seashells for clothes or what?" Kasumi abruptly changed the topic.

Arisa's eye twitched with indignation. "Wh-what? We don't do that! Mermaids have a sense of fashion too ,you know? We're not what the public portrays us as!"

" Okay… so do you think it's possible for me to become a mermaid?" Kasumi moved on to her next question.

" I swear… every question you ask just keeps getting weirder and weirder. No, it's not possible of course! You can't just suddenly replace your legs with a tail!"

" Awww. I was hoping if I could." Kasumi pouted, a little dispirited. " Then could I go into your kingdom? I would like to-

" No, no and of course not! We mermaids are actually forbidden to make contact with humans.I risked my neck to help you. If my grandmother finds out about this, she'll… she'll be very angry!" Arisa responded.

" But you still did help me. That's really sweet of you, A-ri-sa~. "Kasumi teased, hugging the mermaid. 

" Eugh! Get off me! You're heavy!" She complained as Kasumi embraced her.

" Okay… Ack! Aa-chan would be looking for me! She'll be so worried! I gotta get back now!" Kasumi hit upon another realisation and plunged into the knee-deep water.

"Thank you for saving me,Arisa! I hope we meet again!" She waved back to the mermaid before waddling out of the cave.

"You better not tell anyone about this! " She warned. "And... I hope we do." A sad smile emerged on Arisa's face. There was little to no chance of seeing Kasumi again, and she knew that fact. The cave she was sitting in only opened to mermaids,and to those with either special permission or a magical aliment. Kasumi had none of that sort, there was no way she could ever find it again. 

Kasumi approached the shoreline with a huge smile on her face. How lucky was she to have come across another mermaid?

She spotted a figure on the far side of the beach and realised that it was her beloved sister. It seemed like she just got back from her duties as she was still in her sailor uniform.

Sprinting towards her, Kasumi let out a shout to express her happiness. It caught the other girl off guard, and as Kasumi collided with her, they both toppled to the ground. 

"Asukaaaa! I've missed you!" Kasumi gushed, hugging on tight.

" K-kasumi?! Eeeh? Didn't you fall out of the boat yesterday? Why are you- how did you find your way back here?" Asuka struggled to free herself from Kasumi's grip while asking all her questions.

That caused Kasumi to hurriedly let go and spring up. " You will not believe the best thing that happened to me! You know how I said I met a mermaid when I was young and you said it was all some dream but it's not! I found another mermaid that somewhat looked like the same one I met and we talked and there are a lot more mermaids down there! "

Asuka was speechless.

" Di-did you hit your head or something? I already told you mermaids don't-

"But they do! Why won't you believe me, Aa-chan?" Kasumi protested.

Asuka had listened to Kasumi's nonsense way too many times to believe it. There was that one instance when Kasumi managed to make her believe that unicorns existed. The adults told them otherwise. Kasumi tried searching for them, but nothing happened. It was a huge upset for Asuka and she stopped believing in the random things Kasumi would spout.

Unfortunately, her sister was stubborn. 

"Okay, mermaids exist. But you have a bigger problem on your hands than proving their existence." Asuka stood up and brushed herself off.

"... Hehe… Don't worry! I'll settle things with mom and dad!" Kasumi nervously chuckled.

" I hope you do. It's nice to see you back safely, Kasumi." Asuka patted Kasumi's back and walked off towards the staircase that led to town.

Kasumi grinned. "Wait for me, Aa-chan!" She darted towards her sister and thought that maybe letting just one person know about the cave should be fine.


	3. Finding fantasies

Kasumi walked out of the living room nonchalantly. The talk with her parents was not as bad as she feared as they only expressed their concern and banned her from work for a week. It should be fine to go find Arisa, Kasumi thought to herself, because the cave didn't need a boat to access. 

The only problem left was to convince her sister. Kasumi knew that she had told Asuka many untrue things in the past but she was sure that she could prove that mermaids are real. 

Kasumi knew that Arisa would be mad but Asuka could be trusted. She was by far the best secret keeper that Kasumi knew.

Asuka was reading a book in her room, fingers tapping on the table as if waiting for something. 

"Aa-chan!" Kasumi launched herself into her sister's room and flung her hands around her.

"Ka-kasumi! Is there anything you need?" Asuka put her book down. 

Kasumi nodded, eyes twinkling and body trembling from excitement. Asuka took that as a sign to retreat. That was the face she made every time she wanted to show me something weird, Asuka thought, slowly creeping out of her room.

"Eeh? Aa-chan? Wait, I gotta show you something! It's real this time, I swear!" Kasumi clasped her hands together and pleaded.

Asuka realised that Kasumi was more desperate than the other times she asked. Kasumi would probably bug me until I die if I don't comply, she thought. "All right, I'll come. I don't really have anything to do today either."

" Really? Yay! You're the best, Aa-chan!" Kasumi hugged her sister once more before springing out of her room. Asuka followed closely behind.

The sisters walked down the street, Kasumi occasionally pausing whenever she saw something interesting in the shops. They lived in a bustling downtown district and there were many items of Kasumi's interest. That caused Asuka to need to bring her back to reality pretty often. 

When Kasumi wasn't admiring the storefronts, she was babbling about her mermaid friend and the conversation they had.

"-so when I asked her if we could go to her house but she got-

" Kaa-kun!"

Kasumi and Asuka turned around to find a girl with short orange hair. She wore a white sundress with flowers across the top and bottom along with a bright orange jacket. She was holding a brown paper bag in her hands.

Kasumi recognised her immediately. Hagumi Kitazawa, a energetic and cheerful girl who was Kasumi's childhood friend. They both study at Hanasakigawa girls school, and hung out together when they were free.

"Hagu! Are you done with work?" Kasumi greeted her.

"Yup! I saw you and your sister walking around and wanted to bring you a fresh, piping-hot batch of my croquettes!"

" Wah! Thank you so much Hagu! Mmmm~ These smell so nice!" Kasumi accepted the bag of croquettes from Hagumi.

" Hehe… So what are you doing here, Kaa-kun? I thought you had to go do sailor things?" Hagumi asked out of pure curiosity.

" Ah! Me and Aa-chan are finding a mermaid-ack!" Kasumi had momentarily forgotten her promise to Arisa. 

"Mermaids!?" Hagumi shouted in wonder.

She then lowered her voice to a whisper, "Hagu, not so loud! Ummm…. I'm not supposed to say anything about it but…" The brunette looked left and right suspiciously before continuing," Mermaids do exist. I'm bringing Aa-chan along to see her because she wants proof-

"I never said I wanted proof! Kasumi was being annoying, so I came along." Asuka folded her hands, looking away.

" That seems cool! Can I come too, Kaa-kun?" Hagumi asked, thrilled.

" Of course! It's only two more people anyways-

"Can I come too? Finding mermaids seems fun!" Another voice came from behind.

They all turned around, facing a girl with bright blond hair that reached her waist. She wore a red and white striped shirt and blue denim overalls with a ribbon on her wrist.

"Kokoron!" Hagumi and Kasumi both exclaimed.

Kokoro Tsurumaki is a happy-go-lucky girl who is ridiculously rich. She too attends the same school as Kasumi and Hagumi, and is very well known due to her tendency to put on various performances everywhere. Kokoro wants to make the whole world smile, and has steadily made progress through her performances. Be it singing, dancing or puppet shows, she always found a way to make her audience smile.

"Hello! Kasumi! Hagumi! I heard you were looking for mermaids! It's more fun when more people come, right?" Kokoro beamed.

This is bad… Kasumi started to panic. She initially wanted to bring Asuka alone but more and more people are coming.

One more couldn't hurt, right? Kokoro, as far as Kasumi knew, was a trustable person and would not divulge people's secrets to others.

"Kokoron! Please, don't tell anyone about it! I promised her I wouldn't! I can still work things out with her, I think." Kasumi sheepishly twiddled her fingers.

" But if she doesn't want people to see her then won't she be lonely?" 

" ...You're right, Kokoron! I'm sure she's just shy! Let's go see her then! She should be in the cave close to the shore!" Kasumi called out to her friends.

" K-kokoro… I finally… huff…caught up to you… " An exhausted voice sounded behind the group.

" Misaki! You're finally here!" Kokoro didn't sound the least bit surprised.

Kasumi took a while to figure out who she was. Misaki Okusawa, a laid back girl who mainly hangs around Kokoro. She looked rather formal as she was dressed in a black suit and tie.

"Yeah, if only you didn't run off like that. It was really hard to catch up, you know?" Misaki attempted to catch her breath. She then spoke into a black walkie-talkie about Kokoro's location. 

" What's the occasion, Mii-kun?" Hagumi noticed that Misaki's clothing was different.

" This? I thought you knew that I work for the Tsurumaki family as Kokoro's personal assistant and bodyguard. They hired me a while back, so here I am." She replied, like it was nothing out of the ordinary. 

" A bodyguard? Wow! Mii-kun, that's amazing!" Hagumi was in awe. Kasumi shared that sentiment and bombarded Misaki with questions.

"Wait I- No, I don't-" Misaki got flustered by the girl's enthusiasm. "Look, I am coming along. What are you even doing in the first place?" She put off their questions.

Kasumi was the first to answer," Misaki-chan! We are going to find a mermaid! Just please do not mention it to anyone else!"

Misaki was dumbfounded. Mermaids? Are they still kids? Who would believe- she took a look at the group gathered before her and understood. Misaki learned a long time ago that arguing with these types of people would do her no good.

"Ah...alright." Misaki then spotted someone who didn't give off the same energy as the others. She remembered seeing her before. What was her name again? Asumi? Asu… Asuka! Misaki finally remembered, she saw her around Kasumi quite a few times but never actually talked to her. She seems to be the only normal one out of everyone here, Misaki thought.

"Alright! Mermaid scouts! Let's move out!" Kasumi shouted excitedly. 

" Mermaid scouts! That sounds fun!" Kokoro chimed in.

" I'm so excited!" Hagumi leaped into the air, pumping her fist into the sky.

" Is this what you have to go through everyday?" Asuka approached Misaki.

" Yeah. But it's not too bad." Kokoro is one of the few friends Misaki has, and she treasures their friendship.

A while later, the group reached the beach. The beach was a long stretch of sand along the coast, and was a popular spot amongst the youth.

Kasumi led them through the system of rocks at the side of it. It was uninhabited, and made a good place for quiet getaways.

However, as much as Kasumi searched, there was no such existing cave. There were only rocks. Asuka stayed back as she didn't want to get wet.

Kokoro came up with a suggestion as soon as Kasumi told them that the cave was gone. "Maybe, we need to summon it? You said she was shy, right? If we cheer loud enough, she will appear!"

Kasumi and Hagumi readily agreed. The trio then started shouting for Arisa. 

" Please come out, Arisa! I'm sorry for breaking our promise but I really, really want to see you again!" Kasumi pleaded loudly.

" Hello! Im Hagumi and I'm Kaa-kun's friend! We would like to see you please! We won't hurt you!" Hagumi added on.

" Heeey mermaid person! If you come out we can do so many fun things together! We really want to see you! " Kokoro cupped her mouth with her hands and exclaimed. 

Nothing happened.

"Hmm. Maybe it's because Misaki and the other girl didn't join us. Misaki! Other girl! Join us! I bet it'll work!" Kokoro invited Misaki and Asuka.

They were embarrassed but due to the encouragement from the others they gave in.

"Umm please come out so Kasumi will stop bothering me?" Asuka asked, uncertain.

"... Kokoro wants to see you so please show yourself! " Misaki then proceeded to bury her head in her hands. ...I feel so mortified… the people who passed by were staring at us.

Still, nothing happened.

"We just need to keep going! She'll come eventually!" Kasumi rallied everyone, determination blazing in her eyes.

Half an hour passed and no cave or mermaid appeared. Asuka suggested that they go back to the shore for now.

"Let's take a break and rest! We can share some of my family's croquettes!" Hagumi proceeded to take out another batch of croquettes. They were all amazed that it was still fresh and hot.

Kasumi was the only one who was not eating the croquettes but sitting down, deep in thought.

Why didn't Arisa appear? Was it because I broke my promise? Or does she not want to see me? Kasumi's unease swelled with every thought.

What if-

"Kasumi. Here. Eat a croquette. You'll feel better." It was Asuka, hand holding a croquette.

" M'kay. Thanks, Aa-chan." Kasumi took the croquette and stuffed it into her mouth.

"Hey, Aa-chan. Do you think Arisa doesn't want to see me ?" Kasumi felt a little better after finishing the tasty snack.

"Maybe. You are pretty loud and annoying. But you're a good person. She'll show up eventually." Asuka felt weird. Usually she would discourage such thoughts but here she was, telling Kasumi a fable that no one believes. Maybe it was the desperation. Or maybe, mermaids do exist.

That statement by Asuka was enough to rekindle Kasumi's hopes.

"Okay! After this, let's continue searching!" Kasumi faced the sea with newfound tenacity.

She would find Arisa, even if no one else believes her.


End file.
